Question: You are about to conduct a study of the effects of water aerobics for 30 minutes, four times per week on the resting heart rate of elderly women.  You will be comparing the resting heart rate of water aerobic participants to the resting heart rate of the control. Your hypothesis is that the resting heart rate of the water aerobic participants is lower than the resting heart rate of the control group. Other studies of physical activity suggest that you can expect the following:

[Hint:  Take the average of the two variances to estimate the common variance].

μwater aerobics = 73.1        σ2water aerobics = 125.25

μcontrols       = 82.2         σ2controls        = 111.32

Using an equal number of participants, find how many subjects will you need in each group with α = .05 & power = .80?